I would probably look at this from the power you're going with. If you are shooting but using channeling to model that, I'd probably go lawbreaker. If the magic is merely assisting and it's a magical stunt for guns, I would go without the lawbreaker. It's basically about how much you focus on which parts of the shot, is he more doing magic and the gun is a "focus", or is he shooting and the magic is incidental?
I get the feeling that it's the latter.
In that case, a series of magical stunts might be a better fit. Maybe something fitted after inhuman speed? So, for example, you'd be allows to ignore 2 shifts of difficulty due to wind or something along those lines. Pick a few benefits like that and create a power around it. If you want to go full kinetomancy with him later, that's another story, I think.
It could also be interesting to explore the fine line between lawbreaker or not in game. But that's hardly something we can help you with here, that's something for your group to discuss.